Wrong Kid
by Bookphanatic
Summary: "I should have listened to Jace when he said you were just using me. A no good rat-" "ISABELLE!" Isabelle stopped talking. "When did Tate start wearing dresses?" - A misunderstanding causes recently broken up Simon and Isabelle to talk about their relationship. And kidnap a child on accident. AH/AU


**All Rights to Cassandra Clare**

Isabelle Glanced at the carrier next to her. The one year old in the convertible car seat was silently sleeping.

"Is he your first?" Asked a woman as she too, set and identical carrier next to Isabelle's nephew. Isabelle looked over at the woman. She had brown hair and grey eyes and was almost as tall as herself.

"Oh, he not mine. He's my brother's." Isabelle said with a small smile as she looked at Tate. Suddenly the secretary called out to Isabelle.

"Okay let's see, you're here to pick up Tate Lightwood, yes?" Isabelle nodded at the secretary. Her tag read Jia. The door opened behind them and Isabelle turned completely towards the secretary.

"I'll help you in a moment sir, please make yourself comfortable."

"Isabelle? What are you doing here?" Isabelle froze and turned slightly. It couldn't be him, could it? As Isabelle turned, she was proven wrong. Simon stood with his hand in his pockets and his brown hair as messy as always. His glasses were straight on his nose for once and his brown eyes were confused.

"Simon." Simon walked up hesitantly towards her.

"What are you doing here?" Isabelle turned towards the secretary.

"Picking up Tate for Clary." Jia looked up at the two.

"Okay, I'm just going to check out Tate on Isabelle's watch. She was here first." The two nodded. "Isabelle, you're his Aunt correct?" Isabelle nodded. Jia typed a few things then handed Isabelle a pen. "Sign here and you will be good to go." Isabelle signed out and when she turned, Simon already had Tate in his hands and was waiting for Isabelle. She passed by him without a thought. Simon followed hurriedly after her.

"Izzy wait! We need to talk." Isabelle ignored him. "Izzy let me explain. Please." Isabelle turned abruptly.

"There's nothing to talk about. I trusted you Simon. With everything; my parents, my sorrow over Max, Alec's struggles. Everything. Men don't break my hearts. I break theirs." Simon reached for her but Isabelle pulled back and reached for Tate. "Now if you'll excuse me, Clary is expecting me to bring her son home to her." Simon held Tate out of reach.

"Only if you let me talk. Give me five minutes." Isabelle glared icily at Simon. If Simon hadn't dated her for a year, he would have flinched. Now he returned her gaze calmly.

"Fine, but if we're talking, I'm driving." Simon nodded and buckled in Tate's car seat before sitting next to him. Isabelle turned the key in the ignition.

"Talk." Simon sighed as Isabelle backed out of her parking space.

"I know it was a stupid move on my part but Iz, we're really different and having someone who had the same interests was a nice change." He started.

"So now I'm boring to be with?" Isabelle laughed humorlessly.

"No! That's not what I meant to say. I meant..." Tate wailed and Simon turned to look at the newly waking child. Isabelle stopped at a red light as Simon tried to quiet Tate.

Simon looked at through the rearview mirror so he could see Isabelle's eyes.

"Isabelle, please, let's just put this behind us. I can't stand the tension between us and I-"

"You what Simon?" Isabelle glared at him for a moment before moving forward as the green light blinked on. "You want us to be friends so you can run off with Maia and know you got through you're first relationship. None the less breaking someone like, my own, heart?"

"Izzy just let me-"

"No Simon. I can't. In fact, it would probably be better if we just didn't even be friends."

"I can't Iz!" Simon yelled.

"Why not?" She challenged.

"Because I love you!" Silence. Tate's screams were becoming louder. Simon didn't look up at Isabelle. Despite being together for a year, they hadn't uttered the 'L' word yet. Now Simon was blushing though he immediately paled when he realized Tate didn't have brown hair.

"Iz,"

"Just stop, Simon." Isabelle whispered. Simon looked at the blanket that was supposed to be covering Tate.

"Iz, just wait a sec."

"Simon, just shut up please." Simon took off the blanket and took a closer look as 'Tate's' screams became more desperate. The babies watering eyes were blue not green. And it was wearing a dress.

"Isabelle, we brought the wrong kid." The girl wailed louder.

"Simon, I'm really not in the mood. Please calm Tate down."

"Isabelle pull over."

"Simon, I said _shut up._ I can't believe you're stooping this low for my attention." She muttered.

"Isabelle."

"I should have listened to Jace when he said you were just using me. A no good rat-"

"ISABELLE!" Isabelle stopped talking. "When did Tate start wearing dresses?" Isabelle narrowed her eyes at Simon even though he couldn't see her.

"Tate is a boy, Simon. He doesn't wear dresses." Simon sighed exasperated.

"Pull over and I'll show you." Isabelle turned out at the closest exit and parked in a grocery store outlet. As soon as the car was parked, Isabelle unbuckled and opened the opposite door that Simon was not sitting by.

"This isn't Tate."

"That's what I've been trying to tell you." Simon muttered as he took the girl out of her car seat to quiet her.

"We brought the wrong kid." Isabelle's eyes widened. "Oh my god, they're going to think we're felons. That we're kidnappers who molest children." Simon shushed Isabelle.

"Could you be any louder? She's finally calming down." Isabelle shot Simon daggers.

"Do you have the daycare's number?" Isabelle nodded.

"Of course I do, I'm an emergency contact." Simon nodded at her.

"Just call and say that we took the wrong child home and that we currently have a probably year old girl wearing a pink dress and gray leggings." Isabelle already had the phone to her ear as Simon finished. _At least we're talking, _Simon thought as he got out of the car to stretch his legs and move around with to hopefully quiet the screaming child. Isabelle began to speak over the phone.

"Yes, this is Isabelle Lightwood. I was supposed to pick Tate Lightwood up." There was a pause as Isabelle listened.

"Yeah, we sort of took the wrong carrier home and now we have the wrong child." Another pause.

"We are sure. Tate is not a she." Isabelle bit her lip.

"Is her mom aware she took the wrong child home?" Isabelle said in response. Simon watched as she got out of the car to pace. He heard her mutter 'uh huhs' and 'yes'.

Finally as the girl in Simon's arms, and Simon's arms themselves, fell asleep, Isabelle walked towards Simon. She was smiling relieved.

"Tessa and Will are meeting us here." Simon looked up from the baby to Isabelle confused.

"Who the hell are Tessa and Will?" Isabelle looked at the baby in Simon's arms.

"Lucy's parents. Her name is Lucy." She said with a point at the sleeping child. Simon frowned.

"They're not pressing charges?" Izzy laughed.

"I talked to them and turns out they've also been in our shoes." Simon cracked a smile and for a blissful moment, it was just Simon, Isabelle and Lucy.

"If she had black hair she would look like us, sort of." Simon said quietly. He watched Isabelle's content face fall.

"Simon." She started.

"No, hear me out. I love you Isabelle Lightwood. I have since the day I saw you in highschool and Clary told me you were a heartbreaker. Since the days Clary and Jace were dating and you saw me as your best friend's best friend." Isabelle smiled at his word choice. He was completely oblivious.

"I loved you when we graduated and you still didn't see me as anything other than a friend. Then we saw each other at NYU and finally saw something other than friendship." Isabelle stared. "Iz, I mistaked my feelings for Maia as something more, but being alone these past two months, I've only missed you." Isabelle finally looked up from Lucy's face to Simon's. There was no cockiness or stony mask, just sincerity. So Isabelle did what anyone would do and kissed him. Simon immediately responded but couldn't get closer due to the baby in his arms.

"You are an oblivious idiot, Simon Lewis." Simon glanced at Isabelle's dark eyes. If it weren't for the baby between them, they would be less than a hair breaths away. "I was waiting for you to make the first move." Simon froze. Isabelle laughed and took Lucy from Simon's arms. Simon gratefully handed Lucy over to stretch his arms.

"She's pretty heavy." Isabelle glanced at Simon before staring at the sleeping girl in her arms.

"So is Tate." Just then a black car pulled up next to them and a woman closed the door behind her as she quickly walked around the car to Isabelle and Simon. It was the woman from the daycare.

"Oh thank god. Will!" Tessa slowed her walk and took Lucy from Isabelle's arms. Tessa smiled at the two. "Thank you for taking care of her." Simon smiled.

"It was no problem," Isabelle stated as she watched Tessa kiss Lucy's forehead.

"So you were the two child kidnappers who stole my daughter." Said an amused voice as the three looked up. He had messy black hair and blue eyes and a lanky build. He looked like Alec, Isabelle thought. Will was also holding Tate's carrier in his right hand and who could only be his son, in his left hand.

"Will!" Tessa's face was horrified. Izzy and Simon smiled at each other when the words were spoken.

"Don't worry Tess," Will said as he handed Tate to Simon. He glanced at Tate again then at Simon and Isabelle but didn't say anything.

"He's my nephew and his godson." Isabelle explained. Will nodded.

"Can we have the car seat?" Tessa asked. Simon handed Tate over to Isabelle and went to help Tessa.

"Sorry about the inconvenience and thanks for not pressing charges." Simon said. Will shrugged and picked up his fussy son.

"Don't worry about it." His son pulled his hair. "Ow! James stop it, or you won't get to go to Emma's party." James stopped and pouted. Will sighed. "Kids these days. The only enjoyable thing about them is the process of making them." He said with a wink. Isabelle laughed as Simon and Tessa came back with Lucy in her carrier.

"Well thank you again for Lucy." Tessa said as she waved goodbye at the two and took Lucy to their car. Will smiled at them then opened the back seat to buckle his toddler in.

Isabelle turned towards Simon.

"This baby is Tate, right?" Isabelle set the car seat in the back seat and took Tate out. He was sleeping.

"Look for yourself." Tate's golden curls were slightly messy and he was wearing denim overalls over a striped shirt. His feet were clad in converse.

"Definitely him." Simon said and watched as Isabell buckled him in. When she got out, Simon pulled her close and kissed her for a short moment before pulling away. "We don't tell Clary we mistaked her child for a girl. Deal?" For once, Isabelle was speechless and only nodded. Simon smirked and took the keys from her outstretched hand. "I'll drive." Isabelle only smiled.

"Simon, I love you too." Simon felt like he could die of happiness.

**So what'd we think? This was my first Sizzy fanfic so not sure how I did. R&R**


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